Video media plays an important role in communications nowadays and is, in fact, the major contributing factor of the popularity of such technologies as the World Wide Web (WWW), high definition television (HDTV) and video conferencing.
However, in a typical application, transmission of images requires much higher bandwidth than that of, say, textual data or audio signals. Prior art techniques directed to representing and encoding images to efficiently utilize limited bandwidth have been developed. These prior art techniques include well-known progressive image transmission techniques such as those described in: K. Knowlton, "Progressive Transmission of Grey-Scale and Binary Pictures by Simple, Efficient, and Lossless Encoding Schemes," Proceedings of the IEEE, Vol. 68, No. 7, July 1980, pp. 885-896; and A. Frank et al., "Progressive Image Transmission Using a Growth-Geometry Coding," Proceedings of the IEEE, Vol. 68, No. 7, July 1980, pp. 897-909.
In general, in progressive image transmission, a coarse rendition of an image is first transmitted to give a receiver an early impression of the image content. The subsequent transmission provides the image detail of progressively finer resolution. Thus, the receiver may terminate transmission of the image to save bandwidth as soon as the image content is recognized, or as soon as it becomes evident that the image is not of interest. Thus, in progressive transmission, a hierarchy of coarse to relatively fine resolution versions of the image is developed. The coarse resolution version contains important features to which less important details are progressively added to achieve the relatively fine resolution versions.
The above hierarchy may be realized using a hierarchical (or pyramid) data structure to represent an image. For example, one such data structure is described in S. Tanimoto et al., "A Hierarchical Data Structure for Picture Processing," Computer Graphics and Image Processing 4, 1975, pp. 104-119. The hierarchy in question may also be accomplished by encoding an image in a certain manner. For example, using an encoding scheme described in P. Burt et al., "The Laplacian Pyramid as a Compact Image Code," IEEE Transactions on Communications, Vol. Com 31, No. 4, April 1983, one can effectively sample an image with Laplacian operators of many scales. The resulting code representing the image attains a pyramid structure. To achieve the progressive transmission, the topmost level of the pyramid code is sent first to provide an initial coarse image in the receiver. The next level of the code is then transmitted and added to the previous level thereof to enhance the received image, and so on.